The present invention relates to magnetic devices. More particularly, the present invention relates to a recording system including a writer that employs a current through the write element to reduce the coercivity in a portion of a magnetic medium.
Recording heads for use with magnetic storage media typically include a writer and a reader that respectively record and detect magnetic domains in a medium below the head. The writer can include a coil of one or more turns wrapped around a soft ferromagnetic yoke. Writers operate by passing an electric current through the coil, which produces a magnetic field that aligns the yoke magnetization along the field direction. For a longitudinal writer, a magnetic field extends mainly between the pole tips but also partly into the media. For a perpendicular writer, a soft underlayer can be employed in the storage media such that the write field extends between the pole tip and soft underlayer. When the write field exceeds the coercivity and demagnetization field of the media, a domain forms with its magnetization aligned along the write field direction. These domains form the bits of digital data that are detected with the read head.
There are significant physical challenges in trying to achieve an areal density of 1 Tbit/in2 with magnetic recording. The write process is among these challenges, in which magnetic domains, or bits, are created in the media. At these densities, the two primary obstacles facing the write process are the use of materials with large magnetic anisotropy in the media and the lack of soft ferromagnetic materials having Bs>2.4 T. The first obstacle is necessary to ensure thermal stability of the media. The average volume of the grains will have to decrease in order to maintain the same media signal-to-noise ratio, which is roughly set by the number of grains in a bit cell. However, in order to avoid superparamagnetism, the magnetic anisotropy has to increase commensurately so that the grains are ferromagnetic and stable over a time scale of years. The net result is that very large magnetic fields will be needed in order to orient the grains and record bits in the media. Since the write field is intimately related to the saturation moment of the pole tip material in the recording head, very high moment materials will be needed to switch the orientation of the media magnetization. Researchers are already using materials with Bs of about 2.0-2.4 T for 100 Gbit/in2 recording, and the saturation moment requirement for conventional recording at 1 Tbit/in2 is likely to be beyond any known material.
These challenges are well known in the data storage industry and alternative approaches to magnetic recording, such as thermally assisted writing, have already been proposed. However, the best writer technology for 1 Tbit/in2 is still undetermined. For instance, researchers are also investigating ways to switch the magnetization of thin film media that do not rely on thermally assisted processes. These approaches are different in that the alignment of the magnetic field with respect to the media magnetization is significantly different than 0° or 180°. The ultimate goal is to switch the media magnetization using fields that are less than the anisotropy field, Hk.